DTC 25

Code 25 Diagnostic Chart:

Wiring Diagram For MAT/IAT:

CIRCUIT DESCRIPTION:

The Intake Air Temperature (IAT) Sensor is a thermistor that controls the signal voltage to the ECM. The ECM applies a reference voltage (4.0-5.5 volts) on circuit 472 to the sensor. When the air is cold, the sensor (thermistor) resistance is high, therefore the ECM will see a high signal voltage. As the air warms, the sensor resistance becomes less, and the voltage drops.


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. This check determines if the Code 25 is a result of a hard failure or an intermittent condition. A Code 25 will set if the following exist:
a. The MAT/IAT temperature is greater than 135°C (275°F) is detected for time greater than two seconds, with the ignition "ON."


DIAGNOSTIC AIDS:

1. If the engine has been allowed to cool to ambient temperature, coolant temperature and Manifold Air Temperature (MAT) or Intake Air Temperature (IAT) may be checked with a "Scan" tool. The readings should be close to each other.
2. A Code 25 will result if circuit 472 is shorted to ground.
3. If a Code 25 is intermittent, refer to Diagnosis by Symptoms.